Typically, continuous casting of molten aluminum, lead, zinc, and the like are conducted in commercial scale operations using a continuous casting process such as shown in U.S. Pat. Nos. 2,790,216 or 4,054,173. These patents are incorporated herein by this reference. A continuous caster process typically comprises a pair of rotating water cooled caster rolls in which molten metal is routed through a feed tip nozzle into the rotating caster rolls just prior to the line of closest approach of the caster rolls. Heat is rapidly extracted from the molten metal by contact with the water cooled caster rolls and the molten metal freezes as it comes into contact with the water cooled caster rolls. The solid metal is compressed as it passes through the gap between the caster rolls with the thickness of the emerging metal defined by the narrowest spacing between the caster rolls. The thin sheets of metal emerge from the caster rolls with a width of a couple of meters and a thickness of about one to six millimeters (depending upon the actual spacing of the caster rolls). The casting process occurs at approximately one to four meters per minute and each run can last for several days at a time.
An important part of the casting process is the feed tip nozzle which delivers molten metal directly into the gap between the two caster rolls as shown in U.S. Pat. Nos. 4,232,804 and 4,303,181. These patents are incorporated herein by this reference. This process often causes the top face and bottom face of the feed tip nozzle to come directly into contact with the caster rolls. Typically, the feed tip nozzle is made of material harder and more aggressive than the steel caster roll material, such as aluminum oxide or aluminum oxide-silicon oxide fibers The interaction between the moving caster rolls and the hard feed tip nozzle causes scratches to be embedded into the softer caster rolls.
These embedded scratches in the caster rolls, in turn, are applied to the metal after the metal freezes and when the metal passes through and is compressed to conform to the thickness defined by the narrowest gap between the caster rolls. The end result is the production of a continuous sheet of metal with scratch marks typically represented by raised ridges extending above the intended thickness of the sheet of metal as defined by the narrowest gap between the caster rolls.
Currently, the only way to eliminate the scratch marks transferred to the sheet of metal during the roll casting process is to use a feed tip nozzle that has little or no flexing; is able to resist absorption of water; and has the thermal and strength characteristics required to successfully cast nonferrous metals. At the moment, there are no advanced materials on the market that can be used to manufacture such a scratch-free feed tip nozzle.